Mr. Smith resigned in an e-mail message to his bosses at 6:40 a.m. London time, laying out concerns that Goldman’s culture had gone haywire, putting its own interests ahead of its clients.

What the e-mail didn’t say was that about 15 minutes later, an Op-Ed articlehe had written detailing his criticisms was to be published in The New York Times. “It makes me ill how callously people still talk about ripping off clients,” he wrote in the Op-Ed article.

The Op-Ed landed “like a bomb,” inside Goldman, said one executive who spoke on the condition of anonymity.

The article reignited a debate on the Internet and on cable television over whether Wall Street was corrupted by greed and excess. By noon, television crews crowded outside Goldman’s headquarters in Lower Manhattan.

More than three years after the financial crisis, the perception that little has changed on Wall Street — and that no one has been held accountable for the risk-taking that led to the crisis — looms large in the public consciousness. While it was an unusual cry from the heart of a Wall Street insider, many questioned whether it would prompt any change.

Goldman disagreed with the assertions in the Op-Ed article, saying that they did not reflect how the firm treated its clients. Top executives have previously said that despite some rough times of late, clients have stuck with the firm.

Friends of Mr. Smith, who had a list of Goldman’s business principles taped on a wall by his computers in London, say they were not surprised by his public farewell. “He has a really high moral fiber and really cared about the culture of the firm,” said Daniel Lipkin, a Miami lawyer who went to Stanford with Mr. Smith. Mr. Lipkin learned about the Op-Ed on Wednesday from Mr. Smith. “He sounded confident and felt good about his decision to go public,” he said.

Although he isn’t highly paid by Wall Street standards — earning about $500,000 last year, according to people briefed on the matter — Mr. Smith is part of what some Goldman staff members and alumni refer to as a sizable, yet silent contingent within the investment bank. These people are increasingly frustrated with what they see as a shift in recent years to a profit-above-all mentality.

Evidence of this shift, they say, can be seen in the accusations brought by the Securities and Exchange Commission in 2010 that the firm intentionally duped certain clients by selling a mortgage-security product that was designed by another Goldman client betting that the housing market would crash. More recently, a Delaware judge criticized Goldman over the multiple, and potentially conflicting, roles it played in brokering an energy deal. (In both cases, Goldman has denied any wrongdoing.)

The reaction on Wall Street to Mr. Smith’s resignation ranged from those cheering him to others criticizing him for resigning in such a public way. Some within Goldman sought to portray Mr. Smith as a lone wolf — he did not manage anyone — who had failed to become a managing director. (There are about 12,000 executive directors, the equivalent of being a vice president in the United States, but only about 2,500 managing directors among Goldman’s 33,300 employees.)

Others were less surprised. One Goldman client who spoke on the condition of anonymity called the letter “naïve,” saying that the firm had been trading against its clients for years. “Come on, that is what they do and they are good traders, so I do business with them.”

CNBC

Greg Smith, Goldman Sachs

Another Wall Street executive said it was “unforgivable” for Mr. Smith to make his opinions so public and he should have taken them privately to the firm’s senior managers. While Mr. Smith may have tried to raise his concerns with his superiors in meetings, as a fairly junior employee, he did not have much of a voice.

Goldman’s top two executives, Lloyd C. Blankfein and Gary Cohn, said in a letter to employees: “We were disappointed to read the assertions made by this individual that do not reflect our values, our culture and how the vast majority of people at Goldman Sachs think about the firm and the work it does on behalf of our clients. Everyone is entitled to his or her opinion. But it is unfortunate that an individual opinion about Goldman Sachs is amplified in a newspaper and speaks louder than the regular, detailed and intensive feedback you have provided the firm and independent, public surveys of workplace environments.”

But questions about Goldman’s culture persist at a time when the firm — and the rest of Wall Street — are undergoing a transition as the postfinancial crisis framework of regulations known as Dodd-Frank takes hold and as some profitable businesses show little sign of returning to their precrisis highs. It is not a hospitable environment for trading, yet Goldman remains very much a trading firm. Mr. Blankfein, a former gold salesman, comes from the trading business, as does the man who is seen as the most likely to succeed him as chief executive in the next year or two, Mr. Cohn.

Mr. Smith started at Goldman in sales. Born in Johannesburg, Mr. Smith is a grandson of Lithuanian Jews who emigrated to South Africa. His father is a pharmacist and his mother is pursuing a career in social work.

He won a full scholarship to Stanford and after graduating in 2001 landed a spot at Goldman, where he quickly worked his way up in the organization. A table tennis player, Mr. Smith won a bronze medal in the event at the Maccabiah Games in Israel.

He was sent to London about a year ago to sell United States derivative products to European and Middle Eastern investment funds.

What motivated Mr. Smith to come forward now? People close to him said he had high hopes for an internal report that came out after the S.E.C. case, which Goldman settled.

In 2010, Goldman embarked on an internal study that looked at the way it did business. The report reaffirmed the firm’s principles and outlined changes aimed largely at bolstering internal controls and disclosure.

But Mr. Smith thought it fell on deaf ears among senior managers, his friends say.

“I think this was the ultimate act of loyalty,” said Lex Bayer, a friend of Mr. Smith’s from high school in Johannesburg, who went to Stanford with him. “He has always been an advocate for the firm, but he wanted Goldman to do things the right way. In his mind, this was the only way that he could change the culture of the firm.”

He may not be alone inside Goldman. At staff meetings, Goldman’s leadership has been peppered with questions about the firm’s public reputation, say people who have attended those meetings, but who spoke on the condition of anonymity because they were not authorized to speak on the record.

Mr. Smith is making a considerable financial sacrifice in publicly criticizing Goldman. Most Wall Street employees sign nondisparagement and nondisclosure agreements before they join a firm. If Mr. Smith did, Goldman may take legal action and refuse to release stock options he has accumulated. Mr. Smith may also find it difficult to find work on Wall Street after such a public resignation. A spokesman said that Goldman tried to contact Mr. Smith on Wednesday. It is not known whether he responded.

Mr. Smith did not speak publicly about his decision to leave Goldman. On Wednesday, Mr. Smith received messages of support from clients of Goldman.

“You do not know me, but I am a client of Goldman Sachs,” one of them said. “We trade a lot with Goldman and we know that we have to be very careful when we do so,” the person said. “We understand your message.”

People who have spoken to Mr. Smith said that he was flying back to New York on Wednesday night to see his family and friends. These people say Mr. Smith still has no concrete plan for what to do next. He tells friends that he wants to effect change in Goldman’s business practices, although it is unclear what that change would be.

Recruiters say it may be tough slogging for Mr. Smith to find work again on Wall Street, at least in the near term.

“There is a rule of thumb when interviewing — you don’t bad-mouth your old boss. No one wants to hear it,“ said Eric Fleming, the chief executive of the Wall Street recruiting firm Exemplar Partners. “You can argue something like this needed to be said, but if you hire the guy who said it you are taking the risk he will do it again.”